KR0138483B1 - Conductive gray in-mold coating - Google Patents

Abstract

A thermosetting mold coating of fiber-reinforced plastic molded parts is disclosed. The thermosetting coating binder consists of at least one polymerizable epoxy oligomer having two or more acrylate groups and at least one copolymerizable ethylenically unsaturated monomer. Since the paint contains graphite and titanium dioxide, a gray coating is obtained. The coating material has good fluidity and coating property during molding, good adhesion, uniform color, and good surface quality and colorability.

Description

Gray conductive mold coating

FIELD OF THE INVENTION The present invention relates to thermosetting paints used for in-mold molding of molded plastics such as polyester resins, vinyl ester resins or poly (ethylene terephthalate) molded articles or parts. In this coating, graphite is used as a total or partial replacement for the conductive carbon black. The white pigment is then included to obtain a coating in the gray conductive mold.

The molded plastic part can be painted in a mold using an electrically conductive paint. The parts can then be electrostatically colored. The coating in the conductive mold obtained when exclusively using carbon black as the conductive pigment is black. In the case of coloring a part with such a black paint with a light paint such as white, a large amount or multiple layers of light paint are required. It is an object of the present invention to form a paint in a lighter colored conductive mold that requires less light paint and can save time and materials for effective coating.

It has been found that light reflective surfaces can be formed by using graphite as the main conductive pigment and producing a paint in a light conductive conductive mold such as gray using a white pigment such as titanium dioxide. These in-mold coatings can be effectively colored with a small amount of light paint.

The thermosetting paint of the present invention is based on a polymerizable epoxy oligomer having two or more acrylate (or methacrylate or ethacrylate) groups, and acrylic acid, methacrylic acid, ethacrylic acid or similar acids are epoxy oligomers. Or by reacting with a resin such as bisphenol A epoxy, tetrabromo bisphenol A epoxy, phenol novolac epoxy, tetraphenylolethane epoxy, dicyclo aliphatic epoxy and equivalents. Mixtures of these epoxy oligomers can be used. The term (alkyl) acrylate is used to define acrylates, methacrylates or acrylates. Among these materials, preference is given to using diacrylate terminated bisphenol A epoxy oligomers. It has a weight average molecular weight of about 500 to about 1,500. Such materials are well known in the art and in the literature, for example as Cargill Resin 1570 (diacrylate ester of liquid bisphenol A epoxy resin). Examples of other suitable materials include Heat resistant Vinyl Ester Resin, M.B. Launikitis, Technical Bulletin, SC: 116-76, Shell Chemical Company, June 1976 and Shell Chemical Company Technical Bulletins SC: 16-76 and C: 60-78.

Copolymerizable ethylenically unsaturated monomers are used to copolymerize and crosslink the polymerizable oligomers. Suitable monomers include styrene (preferably), α-methyl styrene, vinyl toluene, t-butyl styrene, chloro styrene, methyl methacrylate, diallyl phthalate (with styrene or methyl methacrylate, etc.), triallyl cyanurate , Triallyl isocyanurate, divinyl benzene, methyl acrylate and equivalents or mixtures thereof. The unsaturated monomer is used in an amount of about 80 to about 160 parts by weight, preferably about 80 to about 120 parts by weight, per 100 parts by weight of the polymerizable epoxy oligomer. For further copolymerization and crosslinking, and to improve the hardness of the resulting coating,

Monoethylenically unsaturated compounds having a group of, at least one —NH ₂ , —NH— or —OH group are used in the mold paint. Examples of such monomeric compounds are hydroxyl propyl methacrylate (preferred), hydroxyethyl methacrylate, hydroxy ethyl acrylate, hydroxy ethyl crotonate, hydroxypropyl acrylate, hydroxy polyoxycropylene acrylic Latex, hydroxy polyoxypropylene methacrylate, hydroxy polyoxyethylene methacrylate, acrylamide, methacrylamide, N-hydroxymethyl acrylamide, N-hydroxymethyl methacrylamide and the like and mixtures thereof. . These compounds are used in an amount of about 10 to 120 parts by weight, preferably about 10 to 60 parts by weight, per 100 parts by weight of the polymerizable epoxy oligomer.

Adhesives include various polymers or copolymers formed from alkyl methacrylates in which the alkyl moiety has 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, preferably 1 or 2 carbon atoms, ie methyl or ethyl. In other words, preferred polymers are methyl methacrylate, ethyl methacrylate and the like. The molecular weight of the polymer is generally given in terms of the intrinsic viscosity measured at 20 ° C. using a No. 50 Cannon-Fenske viscometer, ie the intrinsic viscosity of a solution containing 0.25 g of polymer and 50 ml of methylene chloride. . The intrinsic viscosity of such polymers is about 0.15 to 1.3, preferably about 0.2 to 0.6. Such alkyl methacrylate polymers are known in the art and are commercially available from Dupont under the trademark ELVACITE. Other preferred adhesives are polyvinyl acetates having a molecular weight of about 50,000 to 200,000, preferably about 80,000 to 150,000.

The amount of the adhesive in the paint of the present invention is 30 parts by weight or less, preferably 25 parts by weight or less, preferably 20 parts by weight or less per 100 parts by weight of the epoxy polymerizable oligomer.

As the release agent as well as the secondary curing accelerator, zinc salts of various fatty acids having 10 or more carbon atoms can be used. Fatty acids are well known. Reference: Organic Chemistry, Fieser and Fieser, D.C. Health and Company, Boston, 1944, p88, 381-390, 398 and 401, Hackh's Chemical Dictionary, Grant, McGraw Hill Book Company, New York, 1969, p261, and Whittington's Distionary of Plastics, Whittington, Technomic Publishing Co., Inc , Stamford, Conn., 1968, p35, 102 and 261, all references cited therein. Mixtures of zinc salts of fatty acids can be used, examples of some zinc salts are zinc phthalate, zinc stearate, zinc ricinoleate and the like. Preference is given to using zinc salts of saturated fatty acids such as zinc stearate. The zinc salt is used in an amount of about 0.2 to 5 parts by weight, preferably about 0.2 to 2.5 parts by weight, per 100 parts by weight of the polymerizable epoxy oligomer.

Optionally, calcium salts of fatty acids having 10 or more carbon atoms may also be used as mold release agents in the in-mold paints and for controlling the rate of cure. Fatty acids such as those described above are well known. Mixtures of calcium salts of fatty acids can also be used. Examples of some calcium salts are calcium stearate, calcium palmitate, calcium oleate and the like. Preference is given to using calcium salts of saturated fatty acids such as calcium stearate. This calcium salt may be used in an amount of about 0.2 to 5 parts by weight per 100 parts by weight of the polymerizable epoxy oligomer.

Accelerators are used for peroxide initiators and are materials such as desiccants, for example cobalt octoate (preferably). Other materials that can be used are zinc naphthenate, lead naphthenate, cobalt naphthenate and manganese naphthenate. Soluble Co, Mn and Pb salts of linolenic acid can also be used. Mixtures of promoters may also be used. The accelerator is used in an amount of about 0.01 to about 1 part by weight, preferably about 0.1 to about 0.5 part by weight, per 100 parts by weight of the polymerizable epoxy oligomer.

In the mold coating, in order to impart conductivity, graphite is added in an amount of about 5 to about 150 parts by weight, preferably about 20 to about 85 parts by weight, preferably about 40 to about 70 parts by weight, per 100 parts by weight of the polymerizable epoxy oligomer. Use in quantity. The graphite may be any including mined graphite and synthetically produced graphite. The mined graphite contains various impurities. Mined graphite useful in this embodiment typically contains from 60 to 100% by weight of graphite and 0 to 40% by weight of ash, considered to be impurities. Preferred graphites have a small particle size for producing soft molding compositions. Preferred graphite has a particle size of less than the pore size in a 100 mesh sieve, preferably less than the pore size in the 325 mesh sieve, preferably an average particle size of from about 5 to about 30 μm, or wherein the particles are about 15 μm. Ideally.

Conductive carbon black may optionally be used in the composition. Conductive carbon black can greatly reduce the amount of graphite needed to achieve conductivity. The amount of conductive carbon black used in the mold paint is about 15 parts by weight or less based on 100 parts by weight of the polymerizable epoxy oligomer, preferably about 10 parts by weight or less, preferably about 5 parts by weight or less.

A preferred amount of conductive carbon black is about 2 to 10 weight percent, or about 5 weight percent based on the amount of graphite. Conductive carbon black is a high structure carbon black such as Vulcan ^™ XC-72R from Cabot Corporation. This imparts conductivity by forming a continuous carbon network that conducts electricity. Other conductive fillers may also be used.

White pigments are used to lighten the color of the coating in the mold. Examples of white pigments that can be used with or without titanium dioxide are metal titanates, aluminum silicates and calcium silicates, talc, and particles with pores. Preferred white pigments are titanium dioxide and modified titanium dioxide pigments. One preferred titanium dioxide pigment is the Zopaque ^™ RCL-9 of the chloride process rutile type available from SMC. Modified titanium dioxide is also Zopaque ^™ RCL-2 with a coating of alumina and silica oxide available from SCM. When using graphite, small sized pigments having a diameter smaller than the pores of 100 or 325 mesh sieves are preferred. The white pigment is used in an amount of about 5 to about 120 parts by weight, preferably about 10 to about 80 parts by weight, preferably about 15 to about 50 parts by weight, per 100 parts by weight of the polymerizable epoxy oligomer.

The filler is used in the mold paint in an amount of about 20 to about 100 parts by weight, preferably about 20 to about 80 parts by weight, per 100 parts by weight of the polymerizable epoxy oligomer. Examples of fillers are clay, MgO, Mg (OH) ₂ . CaCO ₃ , silica, calcium silicate, mica, magnesium silicate, aluminum hydroxide, barium sulfate, talc, hydrous silica, magnesium carbonate and mixtures thereof. Fillers should generally be of small particle size. Of these, talc is preferred. Fillers can be used to impart the desired viscosity and fluidity to the in-mold paints for molding and assist in the desired physical properties in the resulting thermoset mold coatings. Fillers may also improve adhesion. However, the use of too large amounts of fillers results in high viscosity, which can cause flow and handling difficulties, so care must be taken in using large amounts of fillers.

Optionally, the copolymer- or co-curable diacrylate compound having a weight average molecular weight of about 250 to 5,000 in an amount of about 5 to 120 parts by weight, preferably about 5 to 60 parts by weight, per 100 parts by weight of the polymerizable epoxy oligomer. It can also be used from. Such co-curable diacrylate compounds

(1) at least one polyoxyalkylene glycol-based oligomer having two acrylate groups, and

(2) at least one polyurethane-based oligomer having two acrylate groups, and a mixture of (1) and (2). Although the amounts (1) and (2) shown above can be used, they can reduce hardness at high temperatures, for example 300 ° F., so it is desirable to remove the compound or keep it in an amount of less than 5 parts by weight. Figured out.

Examples of the diacrylate compound (1) include triethylene glycol diacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, polyethylene glycol dimethacrylate. Acrylate or polyoxyethylene glycol dimethacrylate (preferably), polypropylene glycol diacrylate, and the like, and mixtures thereof. These acrylates are formed by reacting polyoxyalkylene glycols such as polypropylene ether glycol with acrylic acid, methacrylic acid and the like. Some of these reactive difunctional materials may contain some OH and / or COOH groups as they may be formed by reaction of unsaturated acids with alcohols.

Examples of the diacrylate compound (2) include polyester urethane diacrylate, polyether urethane diacrylate, polyesterether urethane diacrylate, or other polyurethane oligomers having two acrylate groups. These materials include polyetherdiols (e.g. polypropyleneetherdiol), polyesterdiols (e.g. polyethylene adipatediol), and / or polyetheresterdiols (e.g. polypropylene ether adipatediol) and tolylene diisocyanates, Diisocyanates such as 4,4'-diphenylmethane diisocyanate, hexamethylene diisocyanate and the like are reacted in an amount sufficient to form a diisocyanate terminated polyurethane prepolymer, followed by hydroxypropyl acrylate, hydroxy ethyl acrylate, By reacting with hydroxy ethyl methacrylate or the like to form a diacrylate terminated polyurethane oligomer or polymer. Mixtures of acrylate terminated polyurethane oligomers may also be used. The term used herein: acrylate is to be interpreted to include acrylate as well as methacrylate and acrylate. It is preferable to use a diacrylate polyester urethane oligomer among these materials. It is well known that acrylate terminated polyurethane oligomers are curable, for example by light, ultraviolet light, electron beams and / or infrared light, and the like, and sometimes radiation or radiation curable materials are also mentioned.

The diacrylate compound (1) and / or (2) reduces the hardness of the coating in the mold.

Organic free-radical initiators or free radical generators (catalysts) such as peroxides are used as catalysts for the polymerization, copolymerization and / or crosslinking of ethylenically unsaturated oligomers and other ethylenically unsaturated substances. Examples of free radical initiators include tertiary butyl perbenzoate, tertiary butyl peroctoate in diallyl phthalate, diacetyl peroxide in dimethylphthalate, dibenzoyl peroxide, butylperisobutyrate, di (p − in dibutylphthalate). Chlorobenzoyl) peroxide, di (2,4-chlorobenzoyl) peroxide with dibutylphthalate, dilauroyl peroxide, methylethylketone peroxide, cyclohexanone peroxide in dibutylphthalate, 3,5- Dihydroxy-3,4-dimethyl- 1,2-dioxacyclopentane, t-butylperoxy (2-ethylhexanoate), caprylyl peroxide, 2,5-dimethyl- 2,5-di (Benzoylperoxy) hexane, 1-hydroxycyclohexylhydroperoxide-1, t-butylperoxy (2-ethylbutyrate), 2,5-dimethyl-2,5-bis (t-butylperoxy) Hexane, cumylhydroperoxide, diacetylperoxide, t-butylhydroperoxy , Tert-butylperoxide, 3,5-dihydroxy-3,5-dimethyl- 1,2-oxacyclopentane, 1,1-bis (t-butylperoxy) -3,3,5-trimethyl Cyclohexane etc. and its mixture are mentioned. Sometimes the use of a mixture of initiators is preferred because different rates of decomposition and times are available at different temperatures. Preferred initiators used are tertiary butylperbenzoate. Peroxide initiators should be used in an amount effective to overcome the potency of the inhibitor and cause crosslinking or curing of the ethylenically unsaturated material. Generally, the peroxide initiator is used in an amount of about 5% by weight or less, preferably about 2% by weight or less, based on the weight of the ethylenically unsaturated material used in the mold paint.

The unsaturated materials described above are used in an amount effective to prepare thermoset paints upon curing (eg, polymerization, copolymerization and / or crosslinking).

In order to prevent premature gelation of the ethylenically unsaturated substances and to provide improved shelf life or shelf life, the inhibitor is added to the composition in the desired amount or fed to the raw material before use. Examples of inhibitors include hydroquinone, benzoquinone, p-t-butylcatechol and the like and mixtures thereof.

Optionally, the paint in the mold can be blended with other release agents, antidegradants, UV absorbers, paraffin waxes, solid glass or resin microspheres, thickeners, low shrink additives and the like. These ingredients must be used in amounts sufficient to achieve satisfactory results for the intended purpose. It is not desirable to use materials such as butadiene-styrene block copolymers or fatty alcohol phosphates in the molds of the invention.

Materials such as polyvinyl acetate may be dissolved in reactive monomers such as styrene to facilitate handling. Dilution with styrene may reduce the viscosity of the oligomer. The components of the paint in the mold must be easily mixed and handled at ambient or room temperature or below the polymerization temperature to facilitate pumping and injection into the mold. The components can be warmed or heated before or during mixing and mixed at each stage to facilitate mixing, dispersion and dissolution. In addition, the components may be thoroughly mixed and the residue including the catalyst may be mixed separately, then they may be pumped into the mixing head to mix together and then injected into the mold.

In-mold paints with peroxide initiators or catalysts show weeks of shelf life at room temperature (about 25 ° C.), and those without initiators show months of shelf life at room temperature. It is thus preferred to add the initiator to the composition and mix thoroughly just prior to molding. To obtain reproducible results and to prevent pupil formation, all of the components of the paint in the mold must be kept dry or contain a minimum amount of moisture or moisture content must be adjusted.

The components of the paint in the mold must be thoroughly mixed. Injection molding, compression molding, transfer molding or other forming apparatus or machines can be used in the mold. Molding apparatus and methods can be found in US Pat. No. 4,081,578, which is incorporated herein by reference. In-mold paint is applied to the substrate and cured for about 0.25 to 3 minutes at a temperature of about 270 ° to 330 ° F. (132 to 166 ° C.) and a pressure of about 500 to 1500 or about 1000 psi (35 to 105 or 70 kg / cm ² ). Let's do it.

The manufacturing process and products of the present invention are not only for automotive parts such as grills and headlight assemblies, deck hoods, fenders, door panels and roofs, but also for all recreational regional carriages, water motor prime movers, food trays, appliances and electrical appliances, furniture, machinery It can be used in the manufacture of covers and guards, bathroom parts, structural panels and the like.

The molded plastic substrate may be a molded part based on a thermosetting resin or thermoplastic resin or a glass fiber reinforced plastic (FRP) substrate. Thermosetting resins, such as polyester resins or vinyl ester resins applied to paints in molds, are made from high strength molding compositions (HMC) or highly concentrated molding compounds, as well as sheet molding compounds (SMMC) or bulk molding compounds (BMC) or other FRP materials. Can lose. The FRP substrate may have about 10 to 75 weight percent and preferably about 25 to 35 weight percent or 55 to 60 weight percent glass fibers. Glass fiber reinforced thermoset plastic (FRP) substrates can be rigid or semi-rigid. It is also possible to use other conventional fibers separately or in combination instead of glass fibers. Examples include carbon fibers, boron fibers, graphite fibers, nylon fibers, and the like. The substrate may contain a flexible polymer, such as a flexible portion such as an adipate group in polyester, an elastomer such as styrene-butadiene block copolymer, a plastomer, conventional impact modifiers and the like. Examples of unsaturated polyester glass fiber thermosets are described in Modern Plastics Encyclopedia, 89, mid-October 1988, Vol. 65, No. 11, McGraw-Hill, Inc., New York, and various Shell Chemical Company Technical Bulletins for the aforementioned vinyl esters, which are incorporated herein by reference. Examples of the thermoplastic resin substrate include polyurethane, polyester, polycarbonate, polysulfone, polyamide, polyimide, polyacrylate, poly (alkylene) and polyether. Aromatic groups in these polymers tend to increase their potential use temperature.

The compositions of the present invention generally exhibit good pumpability and flowability in the mold.

The composition can achieve rapid cure within 12-50 seconds at 300 ° F. The composition also shows good adhesion to paints and covers scratches in the mold, as well as good conductive coatings for electrostatic coloring and soluble acrylic lacquers, acrylic dispersion lacquers, aqueous acrylic enamels, high acrylic solids, acrylic enamels, acrylics It can be used as a primer for most paint finishing systems such as non-aqueous dispersions and urethanes.

The invention may be better understood with reference to the following examples, where parts refer to parts by weight unless otherwise indicated.

Example

Paint in the mold is prepared as shown in Table 1. The first four components are added to the reactor and combined under heating at 38 ° C. The next three ingredients are added and blended using a high shear mixer. The carbon black, silica and diacrylate esters are then heated under high shear for 30 minutes and mixed until reaching 44 ° C. When it reaches 44 ° C., the heating is stopped and cooled. Then the last ingredient is added and mixed at 38 ° C. for 1 hour. Formulations 1 to 6 are prepared in this manner.

TABLE 1

All the above amounts are in grams.

^a # 508 Graphite is supplied by Asbury Graphite Mills and contains at least 85% by weight of carbon and passes through a 325 mesh sieve. ^b

# 8535 Graphite is supplied by Superior Graphite. ^c

# 8635 Graphite is supplied by Suoerior Graphite.

Formulations 1 to 6 are then coated in-mold on conventional glass fiber reinforced laminate-molded thermoset polyester-styrene sheets containing 25% by weight of glass fibers at 1000 psi and 300 ° F. for about 45 seconds. In-mold coating test is shown in Table 2.

All of the coatings A-F in the mold showed good adhesion in the Scalpel screening test, and according to the Lansberg meter reading showed excellent conductivity of 165 for electrostatic coloring. In-paint Coating A without a TiO ₂ pigment is used as a control and is black. In-mold coating B, which contains TiO ₂ but does not contain graphite, is lighter in color than A but is not uniform in color and is not suitable for gray primer coating. In-mold coating C, which does not contain graphite but also contains more hydrous magnesium silicate, is not uniform in color. In-mold paintings D, E and F using three different graphites from two different suppliers all form a uniform light gray coating.

TABLE 2

Physical Characteristics of In-mold Painting

^d Adherence is tested by Scalpel screening. ^e

Conductivity is tested with a Ransberg meter from Ransberg Electro-Coating Coporation. The value 120 is suitable for electrostatic coloring.

Although the best mode and the preferred embodiment have been described in accordance with the patent law, the scope of the present invention is not limited thereto but rather limited by the following claims.

Claims (13)

(a) a polymerizable epoxy oligomer having at least two (alkyl) acrylate groups and having a weight average molecular weight of 500 to 1,500, wherein the (alkyl) acrylate is an acrylate, methacrylate or acrylate; (b) 80 to 160 parts by weight of copolymerizable ethylenically unsaturated monomer; (c) 10 to 120 parts by weight of a copolymerizable monoethylenically unsaturated compound having at least one of -CO- and -NH ₂ , -NH- or -OH groups; (d) 5 to 150 parts by weight of graphite, and (e) 5 to 120 parts by weight of white pigments, which are titanium dioxide pigments, modified titanium dioxide pigments or mixtures thereof, wherein the parts by weight based on 100 parts by weight of the polymerization A laminate in which a coating material in a thermosetting mold containing 100 parts by weight of an epoxy epoxy oligomer is adhered to a thermosetting or thermoplastic molding substrate. The amount of the (b) monomer is 80 to 120 parts by weight, the amount of the compound (c) is 10 to 60 parts by weight, the white pigment is present 5 to 80 parts by weight, the The amount is 20 to 85 parts by weight, wherein the thermosetting or thermoplastic molded substrate has 10 to 75% by weight of the laminate. The laminate according to claim 2, wherein the paint in the mold contains 15 parts by weight or less of conductive carbon black, and the thermosetting or thermoplastic molded substrate is an unsaturated polyester thermosetting or vinyl ester thermosetting resin. The laminate according to claim 3, wherein the polymerizable epoxy oligomer of (a) is a diacrylate ester of a liquid bisphenol A epoxy resin, the (b) monomer is styrene and the (c) compound is hydroxy propyl methacrylate. . The laminate according to claim 4, wherein the paint in the mold contains 20 to 100 parts by weight of the filler. 6. The laminate of claim 5, wherein said filler comprises hydrous magnesium silicate. The laminate according to claim 1, wherein the paint in the mold contains 15 parts by weight or less of carbon black and 20 to 100 parts by weight of the filler, and the thermosetting or thermoplastic substrate has 10 to 75% by weight of fibers. The method according to claim 7, wherein the graphite (b) is 20 to 85 parts by weight, the pigment (e) is 10 to 80 parts by weight and comprises a titanium dioxide pigment, a modified titanium dioxide pigment or a mixture thereof, the filler 20 to 80 parts by weight, wherein the substrate is a fiber reinforced thermosetting resin laminate. (a) a polymerizable epoxy oligomer having at least two (alkyl) acrylate groups and having a weight average molecular weight of 500 to 1,500, wherein the (alkyl) acrylate is an acrylate, methacrylate or acrylate; (b) 80 to 160 parts by weight of copolymerizable ethylenically unsaturated monomer; (c) 10 to 120 parts by weight of a copolymerizable monoethylenically unsaturated compound having at least one of -CO- group and -NH ₂ , -NH- or -OH group; (d) 5 to 150 parts by weight of graphite, and (e) 5 to 120 parts by weight of white pigments, which are titanium dioxide pigments, modified titanium dioxide pigments or mixtures thereof, wherein the parts by weight based on 100 parts by weight of the polymerization Based on 100 parts by weight of the epoxy based oligomer). The method according to claim 9, wherein (b) the monomer is 80 to 120 parts by weight, the (c) compound is 10 to 60 parts by weight, the (d) graphite is 20 to 85 parts by weight, and (e) the white pigment A thermosetting paint in which the amount is present in an amount of 10 to 80 parts by weight. 11. The method according to claim 10, wherein the (a) epoxy oligomer is a diacrylate ester of a bisphenol A epoxy resin, the (b) monomer is styrene, the (c) compound is hydroxypropyl methacrylate, and the dioxide A thermosetting paint having 15 to 50 parts by weight of a titanium pigment, a modified titanium dioxide pigment or a mixture thereof. The thermosetting paint according to claim 9, which contains 5 parts by weight or less of carbon black. The thermosetting according to claim 12, wherein the polymerizable epoxy oligomer of (a) is a diacrylate ester of a liquid bisphenol A epoxy resin, the (b) monomer is styrene, and the (c) compound is hydroxypropyl methacrylate. varnish.